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Study Precision

Good Precision - Good Validity

Consider that at the center of the target is the truth and that each shot at the target represents a study you conduct -- a sample of subjects whom you select -- to find the right answer. Here we show five different studies (samples) of the same study design i.e. 5 different samples of the source population. Of course, what you want is this - good validity and good precision.

We say that this is good precision because the differences between the individual samples is very close; there is very little random error. For an explanation of validity, see Validity.

goodp_v.JPG

Poor Precision - Poor Validity

Now consider the target below where each of the different estimates is pretty far away from each other – this is poor precision. For an explanation of validity, see Validity.

poorp_v.JPG

Good Precision - Poor Validity

Consider the target below. We have good precision - the different shots are tightly bunched. For an explanation of validity, see Validity.

poorv_goodprec.JPG

Poor Precision - Good Validity

Consider the target below. We have poor precision - the different shots are widely spaced apart. For an explanation of validity, see Validity.

goodv_poorprec.JPG


Jeff Martin, MD
Topic revision: r4 - 16 Apr 2009 - 17:13:18 - MaryB?
 

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